I love using my kit leftovers. I will often leave the kit on my desk for a week or two after I've completed my design team assignments for the gallery. I find that I get more use out of the leftovers this way, rather than putting everything away immediately.
In this case, I had the new Atlantic collection AND the Planetarium kits on my desk at the same time. There were so many pieces from the kits that I found I could mix with Atlantic. Even a card from the Project Life kit made it onto my layout and matched the yellows in the Atlantic collection perfectly.